arc-over tube failure

[NightPhotographer]

I just got my HD 800 and was about to go for the Chorda Classic-ff amp but everybody kept telling me that I wouldn't do this headphone justice if I went with solid state amps. Since I've never had tube amps, I started reading about them and eventually decided on Crack which seemed to be appreciated by a lot of HD 800 owners. There is just one thing that I am concerned about. Based on my understanding, arc-over tube failure in OTL kills the headphone. Is there any safety measure that I can take to prevent this if I get Crack?

Cheers

[Tom-s]

Don't put any headphones in during power-on, these kind of failure tend to present itself during the power-on. My crack is on 1 min before i insert headphones. *

Pre-amp on -> amp on -> insert headphones
Pull out headphones -> amp off -> pre-amp off

Crack is a great choice! It's so much more than just an amp. It's a journey that starts once you've build it and the modding bug takes hold of you.

*That is, if this applies to crack?

[NightPhotographer]

You mean this is the issue only at power on/off phase? As I said, I've never had a tube amp so my question might sound stupid.

[Paul Birkeland]

There are capacitors between the headphones and the output tube on the Crack, so in the incredibly unlikely event of an arc over tube failure, the headphones are protected.  In OTL speaker amps, often times there is a positive and negative DC supply (or two completely isolated DC supplies), and the output tubes are arranged in a stack, where the signal output is taking from that central junction.  If one output tube shorts, then that power supply is shorted to ground through your speaker, which is quite catastrophic.  Again, this won't happen in a Crack.

The information about plugging and unplugging during startup is completely unrelated.  For what it's worth, I've never bothered unplugging my HD-800's when turning on my Crack, and I pre-ordered mine a long, long time ago.

[NightPhotographer]

@Caucasian Blackplate

Thank you very much for the information. Now, I can place an order for Crack with confidence. I believe you are talking about the output caps (please correct me if I'm wrong). I see some people replace those caps with huge film caps in order to improve the sound quality. Changing the output caps were the last in my list of upgrades but, now, I understand those caps are also important protective elements. Do those film caps also provide better protection? Do you have any suggestion?

[Bacci]

I had considered AMB's ε12 myself in between the amp's output and the headphone jack, but it needs 12 to 30VDC which is nowhere near any voltage points on the Crack (and heaters are AC so voltage doubler wouldn't work). Adding a completely separate PSU for this seemed OTT.

[Paul Birkeland]

Both the film and electrolytic capacitors will provide similar protection.

If you are going to add big film capacitors, there is considerably more space in the Crack-a-two-a to mount them.

There is a modification that you can perform to suppress the startup transient in a Crack, that can be found here: http://bottlehead.com/smf/index.php?topic=2946.0

The Crack 1.1 with the new universal power transformer has implemented this modification in the construction of the amplifier.

-PB